Ammonium nitrate propellant containing amino alkandioate combustion catalyst



3,l89,i% Patented June 15, i965 AMMSNIUM NITRATE PRGEELLANT CGNTAIN- ING AMENO ALKANDIGATE CMBUTEON CATALYST Jack Linsir, Highland, Ind, assignor to Standard Oil Company, (Thicago, 111., a corporation of Indiana No Drawing. Filed Jan. 29, 1958, Ser. No. 712,049 4 Claims. (Ci. 14919) This invention relates to ammonium nitrate-type compositions and particularly a catalyst for promoting the combustion of ammonium nitrate containing compositions.

In gas generation and rocketry usages it is necessary that the gas atiording composition develop gas at a uniform rate; in the art this is spoken of as burning at a uniform rate. In ammonium nitrate compositions which consist essentially of ammonium nitrate particles and an oxidiza-ble organic material (in order to permit the shaping of the composition into a definite configuration or grain) it is necessary to promote the combustion of the composition by the use of a combustion catalyst. Well known catalysts are the inorganic chromium compounds particularly, ammonium dichromate. In the military field the Prussian blues have attained eminence. These and other metallic catalysts have the drawback of forming oxides with very high melting points. It is thought that these solid oxide products in the combustion gases are the cause of nozzle erosion. Nozzle erosion results in erratic change in gas pressure within the gas generator or rocket motor. 7

An object of the invention is an ammonium nitrate composition. A particular object of the invention is an ammonium nitrate composition having low erosive characteristics. A further object is an ammonium nitrate composition whose burning rate is relatively insensitive to variations in burning chamber pressure. Other objects will become apparent in the course of the detailed description.

It has been found that an eminently suitable ammon um nitrate-type composition for gas generator and rocketry usage is obtained with ammonium nitrate as the predominant component between about 10 and 40 weight percent of oxidizable organic material and between about 0.5 and weight percent of alkali metal amino alkandioate having 4-6 carbon atoms as the combustion catalyst. This catalyst burns to form products which are either gas or vapors at the temperature existent in the burning chamber and these products have no appreciable nozzle erosive activity.

The combustion catalyst used in the composition of the instant invention is an alkali metal aminoalkandi-oate havin 46 carbon atoms or a mixture of these materials, such as disodium glutamate and disodium aspartate. Sufficient catalyst must be introduced into the composition to promote the burning of the composition. The amount of catalyst used is also influenced by the rate of burning desired. The more catalyst present the faster the combustion of the composition. It is to be understood that the burning rate is also affected by the particular oxidizable organic material present. In general, the composition will contain between about 0.5 and 15 weight percent of the catalyst. (Hereinafter all percentages are to be understood as weight percent.) With the thermoplastic matrix formers or binders obtained from cellulose esters and oxygenated hydrocarbon plasticizers therefor between about 1 and 6% catalyst produces satisfactory burning rates for typical military gas generation and rocketry usages.

The improved composition of the invention contains ammonium nitrate as the major component. The ammonium nitrate may be either ordinary commercial ammonium nitrate such as is used for fertilizers. This commercial grade material contains a small amount of impurities and the particles are usually coated With moisture resisting material such as paraffin wax. Military grade ammonium nitrate which is almost chemically pure is particularly suitable. The ammonium nitrate is preferably in a finely divided particulate form which may be either produced by prilling or by grinding. The ammonium nitrate is the major component of the gas-generator composition and usually the composition will contain between about and of ammonium nitrate.

In order to permit the shaping of the ammonium nitrate composition into definite configurations a matrix former or binder material is present. When ammonium nitrate decomposes free-oxygen is formed. Advantage of the existence of this free-oxygen is taken and oxidizable materials are used as the binders. These oxidizable organic materials may contain only carbon and hydrogen, for example, high molecular weight hydrocarbons such as asphalts or residuums, and rubbers either natural or synthetic. Or, the oxidizable organic material may contain other elements in addition to carbon and hydrogen for example, Thiokol rubber and neoprene. The stoichiometry of the composition is improved, with respect ,to

smoke production, by the use of oxygenated organic materials as the binders. The hinder or matrix former may be a single compound such as a rubber or asphalt or it may be a mixture of compounds. The mixtures are particularly suitable when special characteristics are to be imparted to the grain which cannot be obtained by the use of a single compound.

The multi-component hinder or matrix former commonly consists of a polymeric base material and a plasticizer therefor. Particularly suitable polymeric base materials are cellulose esters of alkanoic acids containing from 2 to 4 carbon atoms such as cellulose acetate, cellulose acetate butyrate and cellulose propionate; the polyinyl resins such as polyvinylchloride and poylvinyl acetate are also good bases; styrene acrylonitrile is an example of a copolymer which forms a good base material. In general the binder contains between about 15 and 45% of the particular polymeric base material.

The plasticizer component of the binder is broadly defined as an oxygenated hydrocarbon. The hydrocarbon base maybe aliphatic or aromatic or may contain both forms. The oxygen may be present in the plasticizer in either linkage and/or hydroxyl group and/or carboxyl groups; also the oxygen may be present in inorganic substituents particularly nitro groups. In general any plasticizer which is suitable for work with the defined polymers may be used in the invention.

Exemplary classes of plasticizers which are suitable are set out below. It is to be understood that these classes are illustrative only and do not limit the types of oxygenated hydrocarbons which may be used to plas-ticize the polymer.

Di-lower alkyl-phthalates, e.g. dimethyl phthalate, dibutyl phthalate dioctyl phthalate and dimethyl nitrophthalate.

Nitrobenzenes, e.g. nitrobenzene, dinitr-obenzene, nitrotoluene, dinitrotoluene, nitroxylene, and nitrod phenyl.

Nitrodiphenyl others, e.g. nitrodiphenyl ether and 2,4-

dinitrodiphenyl ether.

Tri-lower alk-yl-citrates, e.g. triethyl citrate, tributyl citrate and triamyl citrate.

Acyl tri-lower alkyl-citrates where the acyl group contains 24 carbon atoms, e.g. acetyl triethyl citrate and acetyl tributyl citrate.

area lee Lower alkylene-glycol oxalates, e.g. diethylene glycol oxalate and polyethylene glycol (200) oxalate.

Lower .alkylene-glycol maleates, e.g. ethylene glycol maleate, and'Bis-(diethylene glycol m-onet-hyl ether) male- .ate. a

Lower ialkylene-glycol diglycolates, eg. ethylene glycol diglycolate and diethylene glycol diglycolate.

Miscellaneous diglycolates, e.g. dibutyl diglycolate, dimethylalkyl diglycolate and methylcarbitol diglycolate.

Lower alkylaphthalyl-lower alkylrglycolate, e.g. methyl iphthalyl ethyl glycolate, ethyl phtha'lyl ethyl glycolate and butyl phthalyl butyl glycol-ate.

Di-lower alkyloxy-tetraglycol, e.g. dimeth-oxy tetra glycol and dibutoxy tetra glycol.

Nitro-phenylether of lower al-kylene glycols, e.g. dinitro phenyl ether of triethylene glycol and nitrophenyl ether of polypropylene glycol.

Nitrophenoxy alkanols whereinthe alkanol portion is derived from a glycol having a molecular Weight of not more than about 200. These may be pure compounds or admixed with major component bis(nitrophenoxy) alkane.

A single plasticizer may be used or more usually two or more plasticizers may be used inconjuncti'on. The particular requirements with respect to use will determine not only the polymer but also the particular. plasticizer or combination of plasticizers which are used.

In addition to the basic components, i.e. ammonium nitrate binder and catalyst, the gas-generator propellant composition may contain other materials. For example, materials may be present to improve low temperature ignitability, for instance 'oximes may be present or, asphalt may be present. Surfactants may be present in order to improve the coating of the nitrate with the binder and to improve the shape characteristics of the composition. Various burning rate promoters, which are not catalyst per se, may also be present.

The aromatic hydrocarbon amines are knownto be gas evolution stabilization additives. Examples of these aromatic amines are toluene diamine, diphenyl amine, naphthalene diamine, and toluene triamine. in general the aromatic hydrocarbon amines are used in amounts between about 0.5 and 5 percent. While these aromatic hydrocarbon amines are effective, for severe duties they are frequently not sufficiently effective alone. It has been found that extremely good stabilization is obtained when N-phenylmorpholine additive is used with an aromatic hydrocarbon amine. Because of the plasticizing power of the N-phenylmorpholine it is generally desirable to use the aromatic hydrocarbon amines as the primary stabilizing additive and the N-phenylmor-pholine in an amount needed to obtain the specific stability. In general when aromatic hydrocarbon amines are present bei tween about 0.1 and 1 percent of N-phenylmorpholin-e will be used. 1 Test The composition to be tested for burning rate, pressure exponent and other characteristics required by military 1 specificationswas prepared by first forming a horn ge- 1 neous viscous liquid binder at a temperature of about 1 130 C. Lacquer grade commercial cellulose acetatei anlyzing about 55% of acetic acid was the polymer base. Two plasticizers were used. The one plasticizer contained 1 about 2 par-ts of dini-trophenoxy ethanol and 1 part of i bis(dinitrophenoxy)ethane. This plasticizer mixture was obtained naturally by the reaction of dinitrochlorobenf zene and ethylene glycol in the presence of aqueous sodium hydroxide solution. The other plasticizer was acetyl 1 triethyl citrate. The binder was then cooled to about C. and the ammonium nitrate in fine particles, carbon black and toluene diamine was blended into the binder until a pasty mass was formed. At this time disodium glutamate was introduced into the mixture and worked into the mass :of material. The homogeneous} pasty mass was extruded as rods suitable for use in burning rate tests. Other portions were molded into gas-gem. erator grains for use in large size gas-generation tests. The burning rate tests were conducted in a Crawford bomb pressured at 1000 p.s.i. and 25 C. temperature. 1

The composition consisted of cellulose acetate 11%, the dinitrophenoxy mixture 9%, acetyl triethyl citrate 10%, carbon black 4%, toluene diamine 1%, ammonium' nitrate 62%, and disodium glutamate 3%. This composition had aburning rate of 0.06 inch per second and a pressure exponent of 0.4.

Thus having described the invention, what is claimed 1. A composition consisting essentially of between about 0.5 and 15 Weight percent of alkali-metal aminoalkandioate having 4-6 carbon atoms as a combustion catalyst, ammonium nitrate as the predominant component and between about 10 and 40 Weight percent of oxidizable organic material consisting of a polymeric base selected from the class consisting of cellulose esters of. alkanoic acids containing 2 to 4 carbon atoms, polyvinyl chloride, polyvinyl acetate and styrene-acrylonitrile, and an oxygenated hydrocarbon plasticizer therefor.

2. The composition of claim 1 wherein said catalyst is disodium glutamate.

3. A composition consisting essentially of ammonium nitrate as the predominant component, between about 1 and 6 weight percent of the alkali-metal aminoalk-andioate having 4-6 carbon atoms, between about 20 and 35 Weight percent of a binder consisting of a cellulose ester of an alkanoic acid containing Zto 4 carbon atoms and an oxygenated hydrocarbon plasticizer therefor.

4. A composition consisting of (a) ammonium nitrate, (b) cellulose acetate, about 8l2%, (c) acetyl triethyl citrate, about 7l0%, (d) about 710% of an about 2:1 mixture of dinitrophenoxyethanol and bis(dinitrophenoxy)ethane, (e) carbon, about 34%, (f) toluene diamine, about 1% and (g) disodium glutamate, about 34%.

No references cited.

CA'RL D. QUARFORTH', Primary Examiner.

LEON =D. ROSDOL, Examiner. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF BETWEEN ABOUT 0.5 AND 15 WEIGHT PERCENT OF ALKALI-METAL AMINOALKANDIOATE HAVING 4-6 CARBON ATOMS AS A COMBUSTION CATALYST, AMMONIUM NITRATE AS THE PREDOMINANT COMPONENT AND BETWEEN ABOUT 10 AND 40 WEIGHT PERCENT OF OXIDIZABLE ORGANIC MATERIAL CONSISTING OF A PLOYMERIC BASE SELECTED FROM THE CLASS CONSISTING OF CELLULOSE ESTERS OF ALKANOIC ACIDS CONTAINING 2 TO 4 CARBON ATOMS, POLYVINYL CHLORIDE, POLYVINYL ACETATE AND STYRENE-ACRYLONITRILE, AND AN OXYGENATED HYDROCARBON PLASTICIZER THEREFOR. 